The invention relates to novel glass compositions of the silica-soda-lime type which are intended for the production of flat glass, bottles or flasks. Although the invention is not limited to such an application, it will be described more particularly with reference to motor-vehicle applications.
Windows intended for the motor-vehicle industry are subject to various requirements, especially with regard to their optical properties; these requirements are governed by regulations, for example those regarding the light transmission of a windscreen or those concerned with the user's comfort, for example with regard to energy transmission, or else those concerned with the aesthetic appearance, especially with regard to colour.
Moreover, manufacturers have for some time been focusing on a new requirement--that regarding UV transmission. The purpose of this new tendency is in particular a wish for the best possible protection of the skin from sunlight, which avoids suntanning and sunstroke. Another purpose of this tendency is to reduce fading of fabrics with which the interior of motor vehicles are furnished.
It is known that iron, in its ferric ion form Fe.sup.3+, i.e. in the Fe.sub.2 O.sub.3 form, makes it possible to absorb in the ultraviolet. Moreover, it is known that iron, in its ferrous ion form Fe.sup.2+, i.e. in the FeO form, makes it possible to absorb in the infrared and therefore to absorb energy.
It is thus known that controlling the redox (oxidation-reduction coefficient) of a glass composition makes it possible to regulate the absorption in the ultraviolet compared with that in the infrared with regard to the action of iron.
Moreover, it has already been described, especially in Patent Application WO 94/14716, that cerium oxide CeO.sub.2 has an effect on the UV absorption. However, introducing this oxide increases the cost of the composition very significantly because of the cost of the batch materials which allow this oxide to be introduced.
It has already also been described, especially in Patent U.S. Pat. No. 5,478,783, that titanium oxide TiO.sub.2 also has an effect on the UV absorption. Although the cost of introducing TiO.sub.2 into a glass matrix is less than that of CeO.sub.2, it nevertheless remains very high.
It is also known, especially from document WO 94/14716, to combine the two oxides CeO.sub.2 and TiO.sub.2, still for the purpose of achieving better UV absorption. Of course, such a combination does not allow the additional cost of introducing these oxides into a glass matrix to be reduced.